1. Field of the Invention
The present invention relates to an ink cartridge which supplies an ink to an ink-jet head for performing printing by discharging the ink, and an ink-jet printer including the same.
2. Description of the Related Art
An ink-jet printer is known, in which an ink is discharged from nozzles to recording paper to perform the printing. Such an ink-jet printer is generally provided with a detachable ink cartridge. When an ink-jet head is driven to perform the discharge operation in a state in which the ink is empty in the ink cartridge, then the printing is not only performed, but the air sometimes makes invasion into the ink-jet head. The ink-jet head, into which the air has made invasion, cannot be used in some cases. Therefore, it is necessary to detect the amount of the ink stored in the ink cartridge. A method for detecting the amount of the ink is conceived, in which the amount of the ink is detected by estimating and accumulating the amounts of the ink used every time when the printing is performed. However, any error tends to arise in such calculation. Therefore, it is necessary to stop the use of the ink cartridge with a sufficient margin. As a result, the ink is wasted. Accordingly, the following technique has been suggested (see, for example, Japanese Patent Application Laid-open No. 9-001819, FIG. 7). That is, a float, which has a specific gravity smaller than that of the ink, is arranged on the ink contained in the ink cartridge. The height of the float floating on the ink is detected from the outside to detect the amount of the ink contained in the ink cartridge.
However, according to the technique suggested by Japanese Patent Application Laid-open No. 9-001819, the float is sometimes stuck to the wall surface, and the float is not moved downwardly due to any disturbance such as the surface tension of the ink adhered to the inner wall surface of the ink tank of the ink cartridge. As described above, the technique suggested by Japanese Patent Application Laid-open No. 9-001819 tends to suffer from the influence of the disturbance such as the surface tension of the ink. Therefore, a problem arises such that it is impossible to indicate any correct amount of the ink contained in the ink cartridge.